Fiber-optic communication networks are experiencing rapidly increasing growth in capacity. This capacity growth is reflected by individual channel data rates scaling from 10 Gbps (gigabits per second), to 40 Gbps, to developing 100 Gbps, and to future projections of 1000 Gbps channels and higher. The capacity growth is also reflected by increasing total channel count carried within an optical fiber. Conventional solutions focus almost exclusively on increasing channel spectral efficiency, while maintaining a total spectral occupancy constrained by the spectrum available based on erbium doped fiber amplifier (EDFA) and Raman optical amplifiers. Indeed, EDFA and Raman provide excellent, inexpensive, and low-noise optical amplification and their benefits are hard to ignore. Thus, the industry focus has been on developing high performance, spectrally efficient transmitters and receivers, with recent direction on digital signal processor (DSP)-based coherent implementations with Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (QAM), etc. formats.
Accordingly, conventional solutions to capacity problem focus on expensive and power-hungry transmitter and receiver hardware, frequently requiring a combination of both EDFA and Raman amplification to lower optical noise figure, and may require new fiber types such as ultra-low loss and high effective area fibers. All of these increase overall network cost and complexity. Further, Metro scale networks generally require channel Add/Drop at every node, which is accomplished today with Optical add-drop multiplexing (OADM) implementations. When additional requirements of dynamic provisioning, protection, restoration, etc. are added, the OADM nodes become more complex and difficult to control for analog optical signals. What is desired is an alternative approach to achieving high capacity over fiber-optic links, while providing frequent add/drop access to fractions of the network bandwidth.